Such systems, which are also referred to in technical language as the Adblue system, can be used in automotive engineering to reduce nitrogen oxides contained in the exhaust gas flow to nitrogen. This reduction takes place by the metered supply of an aqueous urea solution from a supply tank, via a supply device, to the exhaust gas flow. Ammonia is obtained from the urea by hydrolysis. The ammonia functions as a selective reducing agent in the exhaust gas flow. To optimize the efficiency of the reduction, the aqueous urea solution is supplied to the exhaust gas flow in a metered manner by a pump, which pump is controlled by a control device in a load-dependent manner.
The water content of the urea solution, which functions as an additional working substance, has a disadvantageous effect on the operating behavior. If the aqueous solution should freeze, the entire system could fail, in particular as a result of the pump and the supply device connected thereto becoming damaged or destroyed. This risk exists, in particular, during immobilization times at frost temperatures.